Hologram and method of and apparatus for producing the same

ABSTRACT

A duplicating photosensitive material film is brought into close contact with an ND glass reduced in thickness so as to become flexible or a flexible sheet or an ND glass coated with a cushioning layer through an optical contacting liquid containing a surface active agent. In addition, a spacer is interposed between a hologram original plate and a duplicating photosensitive material, and a space defined by the spacer is filled with an optical contacting liquid, thereby regulating the thickness of the optical contacting liquid layer with the spacer. Therefore, when pressure is applied, the optical contacting liquid is uniformly pressed, so that it can be made uniform and thin in thickness. Accordingly, it is possible to prevent a failure of duplication of a hologram image due to undesirable flow of the optical contacting liquid. In addition, the wettability of the optical contacting liquid improves, so that it is possible to prevent trapping of air and foaming and to make the optical contacting liquid uniform and thin in thickness. Thus, it becomes possible to duplicate a hologram image excellently. In addition, a cushioning layer is provided on the inner side of an AR coated ND glass or on the upper side of a photosensitive material film, and another cushioning layer is provided on the side of an original plate protecting glass which is closer to the optical contacting liquid or on the lower side of the photosensitive material film. With this arrangement, even if dust enters, it can be effectively held inside the cushioning layers. Thus, it is possible to prevent undesirable flow of the optical contacting liquid and lifting of the film due to dust and hence possible to perform duplication effectively without any hindrance. Also disclosed is a hologram producing apparatus which includes mechanisms for feeding and taking up a duplicating photosensitive material film, and a contacting liquid dropping mechanism. The apparatus further includes a mechanism for nipping an excess of contacting liquid dropped, a mechanism for drying the contacting liquid attached to the exposed duplicating photosensitive material film, a mechanism for positioning the film, etc.

This is a divisional of application Ser. No. 08/039,854 filed on Mar.30, 1993, now U.S. Pat. No. 5,453,388.

BACKGROUND OF THE INVENTION

The present invention relates to a hologram and a method of andapparatus for producing the same. Here, it should be noted that the term"produce" as used in the present invention includes "duplicate".

More specifically, the present invention relates to a hologram producedby applying laser light split into two beams to a recording unitincluding a photosensitive material film placed in close contact with ananti-reflection coated glass or an ND glass or an anti-reflection coatedND glass through an optical contacting liquid, and also relates to amethod of producing the hologram.

A hologram original plate has heretofore been duplicated by applying alaser beam to the hologram original plate placed in close contact with aphotosensitive material so that diffracted light from the original plateand the incident light interfere with each other in the photosensitivematerial, thereby recording a hologram image of the original plate inthe photosensitive material. In this process, in order to prevent thedisorder of the image due to the back reflection component, an opticalcontacting liquid that is substantially equal to the original plate inrefractive index is interposed between the original plate and thephotosensitive material, thereby enhancing the adhesion and preventingback reflection during the duplication of the hologram image.

Incidentally, the optical contacting liquid, which is interposed betweenthe glass and the photosensitive material film, is difficult to applywith a uniform thickness because of fluidity, vibration, etc. Inparticular, when a large amount of contacting liquid is applied, it islikely to take a long time from the application of the liquid to thesettlement of its flow, which interferes with the production of ahologram. In addition, even if production or duplication of a hologramis carried out in a clean room, it is impossible to completely eliminateforeign substances (dust) of the order of 10 μm in diameter which arecarried in from the outside when the operator enters the room, or whenthe materials are fed in, and attached to the film and/or the glass.Such foreign substances undesirably lift the film, resulting in regionswhere the hologram cannot be recorded due to the flow of the opticalcontacting liquid around the foreign substances. In addition, since thefilm is pressed by the foreign substances, the hologram produced or madeby duplication is attended with a large number of defects(depression-shaped defects) with which a reconstructed image of thehologram looks as if there were depressions of the order of severalhundred μm to several mm in diameter.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a hologram in whichthe optical contacting liquid is made uniform and thin in thickness andwhich can be duplicated without any hindrance even if a foreignsubstance is mixed in.

It is another object of the present invention to provide a method of andapparatus for producing a hologram, whereby the optical contactingliquid is made uniform and thin in thickness and a hologram can beproduced without any hindrance even if a foreign substance is mixed in.

It is still another object of the present invention to make it possibleto prevent mingling of air during production of a hologram.

It is a further object of the present invention to allow an opticalcontacting liquid to become uniform in thickness within a short time andto enable a hologram to be produced excellently and efficiently.

To these ends, the present invention provides a hologram produced byapplying laser light split into two beams to a recording unit includinga photosensitive material film placed in close contact with ananti-reflection coated glass or an ND (Neutral Density) glass or ananti-reflection coated ND glass through an optical contacting liquid. Inthis arrangement, a cushioning layer made principally of a polymer ofhigh elasticity is provided either on the side of the anti-reflectioncoated glass or ND glass or anti-reflection coated ND glass which iscloser to the film or on the side of the film which is closer to theglass so that a mingling foreign substance is buried in the cushioninglayer, thereby reducing the incidence of depression-shaped defects.

In addition, the present invention provides a duplicate hologram whichis recorded on a duplicating photosensitive material film by applyinglaser light to a duplicating system in which an original plate unit,which includes an original plate hologram supported by a substrate andan original plate protecting glass bonded to the upper side of theoriginal plate hologram, is brought into close contact with aduplicating unit which includes the duplicating photosensitive materialfilm placed in close contact through an optical contacting liquid withan anti-reflection coated glass or an ND glass or an anti-reflectioncoated ND glass or an ND glass placed in close contact with ananti-reflection coated glass through an optical contacting liquid. Inthis arrangement, a cushioning layer made principally of a polymer ofhigh elasticity is provided either on the side of the original plateprotecting glass which is closer to the duplicating unit or on the sideof the duplicating photosensitive material film which is closer to theoriginal plate unit so that a foreign substance which may mingle duringduplication is buried in the cushioning layer, thereby reducing theincidence of depression-shaped defects.

In addition, the present invention provides a method of producing ahologram by applying laser light split into two beams to a recordingunit including a photosensitive material film placed in close contactwith an anti-reflection coated glass or an ND glass or ananti-reflection coated ND glass through an optical contacting liquid. Inthis method, a cushioning layer made principally of a polymer of highelasticity is provided either on the side of the anti-reflection coatedglass or ND glass or anti-reflection coated ND glass which is closer tothe film or on the side of the film which is closer to the glass so thata foreign substance which may mingle during the production of thehologram is buried in the cushioning layer, thereby reducing theincidence of depression-shaped defects.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate and an original plateprotecting glass bonded to the upper side of the original platehologram, is brought into close contact with a duplicating unit whichincludes the duplicating photosensitive material film placed in closecontact through an optical contacting liquid with an anti-reflectioncoated glass or an ND glass or an anti-reflection coated ND glass or anND glass placed in close contact with an anti-reflection coated glassthrough an optical contacting liquid. In this method, a cushioning layermade principally of a polymer of high elasticity is provided either onthe side of the original plate protecting glass which is closer to theduplicating unit or on the side of the duplicating photosensitivematerial film which is closer to the original plate unit so that aforeign substance which may mingle during duplication is buried in thecushioning layer, thereby reducing the incidence of depression-shapeddefects.

In addition, the present invention provides a hologram producingapparatus including a device for supplying a duplicating film, a devicefor dropping or coating a contacting liquid on a hologram original platesupported by a support and on the duplicating film, and a roller forsmoothing the supplied contacting liquid. The apparatus further includesa device for pressing a flexible layer against the film through thecontacting liquid, a laser light source for applying laser light fromabove the flexible layer, and a device for drying the exposedduplicating film.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate and an original plateprotecting glass bonded to the upper side of the original platehologram, is brought into close contact with a duplicating unit-whichincludes the duplicating photosensitive material film placed in closecontact with an anti-reflection coated glass or an ND glass or ananti-reflection coated ND glass through an optical contacting liquid. Inthis method, a surface active agent is added to the optical contactingliquid so as to increase wettability of the optical contacting liquidwith respect to the base material, thereby reducing the incidence ofdepression-shaped defects caused by air trapped during duplication.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate and an original plateprotecting glass bonded to the upper side of the original platehologram, is brought into close contact with a duplicating unit whichincludes the duplicating photosensitive material film placed in closecontact with an anti-reflection coated glass or an ND glass or ananti-reflection coated ND glass through an optical contacting liquid. Inthis method, the optical contacting liquid has a viscosity in the rangeof 100 cps to 10,000 cps so that a foreign substance which may mingleduring duplication is buried in the viscous optical contacting liquid,thereby reducing the incidence of depression-shaped defects caused byforeign substances.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate and an original plateprotecting glass bonded to the upper side of the original platehologram, is brought into close contact with a duplicating unit whichincludes the duplicating photosensitive material film placed in closecontact with an anti-reflection coated glass or an ND glass or ananti-reflection coated ND glass through an optical contacting liquid. Inthis method, the optical contacting liquid is a liquid substancecomprising an ionizing radiation curing polymer, monomer or the like sothat the optical contacting liquid is polymerized through a curingreaction caused by irradiation with ionizing radiation during or afterthe duplication process, thereby making it separable from the film.

In addition, the present invention provides a hologram producing methodwherein a hologram original plate and a duplicating photosensitivematerial are brought into close contact with each other through at leasta rigid spacer and an optical contacting liquid injected into a spacedefined by the spacer, and laser exposure is carried out so thatdiffracted light from the hologram original plate and incident lightinterfere with each other in the duplicating photosensitive material,thereby recording a hologram image in the duplicating photosensitivematerial.

In addition, the present invention provides a hologram producing methodwherein a hologram original plate and a duplicating photosensitivematerial are brought into close contact with each other directly or witha transparent member interposed therebetween, and an anti-reflectioncoated glass or an ND glass or an anti-reflection coated ND glass isplaced on either the hologram original plate or the duplicatingphotosensitive material in close contact with each other through a rigidspacer and an optical contacting liquid injected into a space defined bythe spacer. Then, laser light for exposure is applied from the glassside so that diffracted light from the hologram original plate andincident light interfere with each other in the duplicatingphotosensitive material, thereby recording a hologram image in theduplicating photosensitive material.

In addition, the present invention provides a hologram producing methodwherein a hologram original plate and a duplicating photosensitivematerial are brought into close contact with each other through at leasta spacer and an optical contacting liquid injected into a space definedby the spacer, and an anti-reflection coated glass or an ND glass or ananti-reflection coated ND glass is placed on either the hologramoriginal plate or the duplicating photosensitive material in closecontact with each other through a spacer and an optical contactingliquid injected into a space defined by the spacer. Then, laser lightfor exposure is applied from the glass side so that diffracted lightfrom the hologram original plate and incident light interfere with eachother in the duplicating photosensitive material, thereby recording ahologram image in the duplicating photosensitive material.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate, is brought into closecontact with a duplicating unit which includes the duplicatingphotosensitive material film placed in close contact with ananti-reflection coated glass or an ND glass or an anti-reflection coatedND glass through an optical contacting liquid. In this method, thethickness of the anti-reflection coated glass or ND glass oranti-reflection coated ND glass is set in the range of 0.1 mm to 1.5 mmso that the glass is flexible.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate, is brought into closecontact with a duplicating unit which includes the duplicatingphotosensitive material film placed in close contact with a polymericmaterial sheet through an optical contacting liquid. In this method, thesheet is flexible and equal to the optical contacting liquid inrefractive index.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate, is brought into closecontact with a duplicating unit which includes the duplicatingphotosensitive material film placed in close contact with ananti-reflection coated glass or an ND glass or an anti-reflection coatedND glass through an optical contacting liquid. In this method, acushioning layer is provided on the side of the anti-reflection coatedglass or ND glass or anti-reflection coated ND glass which is closer tothe optical contacting liquid.

In addition, the present invention provides a hologram producing methodin which an image of an original plate hologram is recorded on aduplicating photosensitive material film by applying laser light to aduplicating system in which an original plate unit, which includes theoriginal plate hologram supported by a substrate and an original plateprotecting glass bonded to the upper side of the original platehologram, is brought into close contact with a duplicating unit whichincludes the duplicating photosensitive material film placed in closecontact with an anti-reflection coated glass or an ND glass or ananti-reflection coated ND glass through an optical contacting liquid. Inthis method, a cushioning layer is provided either on the side of theanti-reflection coated glass or ND glass or anti-reflection coated NDglass which is closer to the optical contacting liquid or on the upperside of the photosensitive material film, and another cushioning layeris provided either on the side of the original plate protecting glasswhich is closer to the duplicating unit or on the lower side of thephotosensitive material film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explanation of one example of a method ofduplicating a hologram according to the present invention, in which acushioning layer is provided.

FIGS. 2(a) and 2(b) are views for explanation of a film laminatingmethod.

FIG. 3 illustrates the arrangement of a hologram duplicating apparatusaccording to the present invention.

FIG. 4 is a graph showing the results of a stylus force-displacementtest carried out on some examples of cushioning layers.

FIGS. 5(a) and 5(b) are photographs showing a reconstructed image oftraces of foreign substances recognized when a hologram produced byusing a cushioning layer of the present invention is observed with anoptical microscope.

FIG. 6 is a view for explanation of another example of the hologramduplicating method according to the present invention.

FIGS. 7(a) and 7(b) are views for explanation of the wettability of anoptical contacting liquid employed in the present invention.

FIGS. 8(a) and 8(b) are views for explanation of the wettability of anoptical contacting liquid employed in the present invention.

FIG. 9 is a sectional view of a layer configuration in which a sheet ofa polymeric material is employed.

FIG. 10 is a sectional view of a layer configuration in which acushioning layer is provided.

FIGS. 11 to 13 are views for explanation of a method of duplicating atransmission hologram.

FIGS. 14 to 16 are views for explanation of a method of duplicating areflection hologram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a hologram duplicating method according to thepresent invention, which employs a flexible ND glass provided with ananti-reflection (AR) coating. On the AR coated ND glass 1, an originalplate supporting glass 3 is placed in close contact with it through anoptical contacting liquid 2. An original plate film 4 is supported bythe supporting glass 3, and an original plate protecting glass 6 isbonded to the original plate film 4 with an optical adhesive 5, therebyforming an original plate unit. On the original plate unit, aduplicating photosensitive material film 8 is placed with a cushioninglayer 16 and an optical contacting liquid 7 interposed therebetween, andan optical contacting liquid 9, a cushioning layer 15, and an AR coatedND glass 13 are successively stacked up on the film 8, thereby forming aduplicating unit.

Thus, according to the present invention, the adhesive cushioning layer15 is provided on the inner side of the AR coated ND glass 13, and thecushioning layer 16 is provided on the side of the original plateprotecting glass 6 which is closer to the optical contacting liquid 7.The cushioning layers 15 and 16 are formed by employing gelatin used forphotography, case in used in the process for producing semiconductors,an adhesive polymeric material, etc. By virtue of the presence of thesecushioning layers 15 and 16, force acts uniformly on the opticalcontacting liquid, so that the optical contacting liquid can be madeuniform and thin in thickness. In addition, if dust is mixed in, it isheld inside the cushioning layer 15 or 16. Thus, it is possible toprevent undesirable flow of the contacting liquid and lifting of thefilm by foreign substances. Accordingly, duplication of the hologram canbe effected without any hindrance. It should be noted that the sameadvantageous effects can also be obtained by an arrangement in which thecushioning layer 15 is replaced by a similar cushioning layer providedon the upper side of the photosensitive material film 8, and thecushioning layer 16 is replaced by a similar cushioning layer providedon the lower side of the photosensitive material film 8.

As the cushioning layers, various kinds of material can be used asfollows:

The cushioning layers may be polymer layers formed of a binder polymer,or a binder polymer containing a plasticizer.

Examples of binder polymers usable in the present invention includenatural polymers and synthetic polymers.

Examples of preferable natural polymers are proteins such as albumin,globulin, casein, collagen, gelatin, elastin, keratin, fibroin, etc.,polysaccharides such as agar (agarose and agaropectin), alginic acid,chitin, chitosan, cellulose, starch, lignin, etc., and natural rubber.

Among these natural polymers, casein, gelatin, and natural rubber, whichare excellent in optical properties and coating properties, areparticularly preferable.

Examples of preferable synthetic polymers areacrylate-styrene-acrylonitrile (AAS) copolymer,acrylonitrile-butadiene-styrene (ABS) copolymer, chlorinatedpolyethylene-acrylonitrile-styrene (ACS) copolymer, acrylic estercopolymer, olefin-vinyl alcohol copolymer, alkyd resin, amino resin,bismaleimide-triazine resin, cellulose acetate (CA), cellulose acetatebutyrate (CAB), ethyl cellulose (EC), hydroxyethyl cellulose,carboxymethyl cellulose, chlorinated polyether, cumarone resin,chlorinated polyethylene, allyl resin, ethylene-α-olefin copolymer,ethylene-vinyl acetate copolymer (EVA), ethylene-vinyl chloridecopolymer, ethylene-vinyl acetate-vinyl chloride copolymer, epoxy resin,furan resin, fluorocarbon resin, ionomer, ketone resin,methacrylate-butadiene-styrene (MBS) copolymer, methacryl-styrenecopolymer, nitrile resin, hydroxybenzoyl polyester, petroleum resin,phenol resin, polyacetal, polyamide, polyamidimide, polyarylate,polyallyl sulfone, polybutadiene, thermosetting polybutadiene,polybutylene, polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, water crosslinkable polyethylene, polyethyleneterephthalate, polyimide, polyamino bismaleimide, methacrylic resin(PMMA), polymethylpentene, polypropylene, polyphenylene oxide,polyphenylene sulfide, polyphenylene sulfone, polysulfone, polystyrene,styrene-acrylonitrile (SAN) copolymer, styrene copolymer,butadiene-styrene copolymer, polyurethane, vinyl acetate resin,polyvinyl acetal, polyvinyl alcohol, polyvinyl chloride, acryl modifiedpolyvinyl chloride, polyvinylidene chloride, silicone, xylene resin,urethane acrylate resin, etc.

Typical polymers usable in the present invention and the refractiveindices and glass transition temperatures thereof will be shown below.

    ______________________________________                                        Polymers             n          Tg (K.°)                               ______________________________________                                        Polyvinylidene fluoride                                                                            1.42       233                                           Polydimethyl silylene (polydimethyl                                                                1.43       146                                           siloxane)                                                                     Polyoxypropylene     1.4495     198                                           Polyvinyl isobutyl ether                                                                           1.4507     254                                           Polyvinyl ethyl ether                                                                              1.4540     230                                           Polyoxyethylene      1.4563     232                                           Polyvinyl butyl ether                                                                              1.4563     218                                           Polyvinyl pentyl ether                                                                             1.4581     207                                           Polyvinyl hexyl ether                                                                              1.4591     199                                           Poly(4-methyl-1-pentene)                                                                           1.459-1.465                                                                              302                                           Cellulose acetate butyrate                                                                         1.46-1.49  322-388                                       Polyvinyl octyl ether                                                                              1.4613     194                                           Poly(vinyl-2-ethyl hexyl ether)                                                                    1.4626     207                                           Polyvinyl decyl ether                                                                              1.4628     211                                           Poly(2-methoxy ethyl acrylate)                                                                     1.463      223                                           Polybutyl acrylate   1.4631     251                                           Poly(t-butyl methacrylate)                                                                         1.4638     333                                           Poly(3-ethoxy propyl acrylate)                                                                     1.465      218                                           Polyvinyl propionate 1.4665     283                                           Polyvinyl acetate    1.4665     305                                           Polyvinyl methyl ether                                                                             1.467      242                                           Polyethyl acrylate   1.4685     249                                           Ethylene-vinyl acetate copolymer (80%-20%                                                          1.47-1.50                                                vinyl acetate)                                                                Cellulose propionate 1.47-1.49  400                                           Cellulose triacetate 1.47-1.48  322-751                                       Polyvinyl methyl ether (isotactic)                                                                 1.4700     242                                           Poly(3-methoxypropyl acrylate)                                                                     1.471      198                                           Poly(2-ethoxyethyl acrylate)                                                                       1.471      223                                           Polymethyl acrylate  1.472-1.480                                                                              283                                           Polyisopropyl methacrylate                                                                         1.4728     354                                           Poly(1-decene)       1.4730     232                                           Polypropylene (atactic; density: 0.8575 g/                                                         1.4735     260                                           cm.sup.3)                                                                     Poly(vinyl sec-butyl ether) (isotactic)                                                            1.4740     254                                           Polydodecyl methacrylate                                                                           1.4740     208                                           Polyoxyethylene oxysuccinoyl (polyethylene                                                         1.4744     244                                           succinate)                                                                    Polytetradecyl methacrylate                                                                        1.4746     201-264                                       Ethylene-propylene copolymer (EPR-rubber)                                                          1.4748-1.48                                                                              140-260                                       Polyhexadecyl methacrylate                                                                         1.4750     288                                           Polyvinyl formate    1.4757     310                                           Polyisobutyl methacrylate                                                                          1.477      333                                           Ethyl cellulose      1.479      316                                           Polyvinyl acetal     1.48-1.50  305                                           Cellulose acetate    1.48-1.50  322-751                                       Cellulose tripropionate                                                                            1.48-1.49  400                                           Polyoxymethylene     1.48       232                                           Polyvinyl butyral    1.48-1.49  322                                           Poly(n-hexyl methacrylate)                                                                         1.4813     268                                           Poly(n-butyl methacrylate)                                                                         1.483      293                                           Poly(n-propyl methacrylate)                                                                        1.484      308                                           Polyethyl methacrylate                                                                             1.485      338                                           Poly(1,1-diethylpropyl methacrylate)                                                               1.4889     268                                           Polymethyl methacrylate                                                                            1.4893     378                                           Poly(2-decyl-1,3-butadiene)                                                                        1.4899     220                                           Polyvinyl alcohol    1.49-1.53  358                                           Polyethylene glycolate methacrylate                                                                1.4903     328                                           Methyl cellulose (low viscosity)                                                                   1.497      423                                           Polyurethane         1.5-1.6    200-400                                       Poly(1,2-butadiene)  1.5000     269                                           Polyvinyl formal     1.50                                                     Cellulose nitrate     1.50-1.514                                                                              326                                           Poly(2-heptyl-1,3-butadiene)                                                                       1.5000     190                                           Poly(2-isopropyl-1,3-butadiene)                                                                    1.5028     221                                           Polypropylene (density: 0.9075 g/cm.sup.3)                                                         1.5030     260                                           Polyisobutene        1.505-1.51 200                                           Polybornyl methacrylate                                                                            1.5059     383                                           Poly(2-t-butyl-1,3-butadiene)                                                                      1.5060     293                                           Polyethylene glycol dimethacrylate                                                                 1.5063                                                   Polycyclohexyl methacrylate                                                                        1.5066     356                                           Guttapercha (β) 1.509      215                                           Polyoxyethylene (high-molecular weight)                                                            1.51-1.54  232                                           Polyethylene (density: 0.914 g/cm.sup.3)                                                           1.51       148                                           Poly(2-hydroxyethyl methacrylate)                                                                  1.5119     328                                           Polybutene (isotactic)                                                                             1.5125     249                                           Guttapercha (α)                                                                              1.514      215                                           Poly(1,3-butadiene)  1.5154     269                                           Poly(2-chloroethyl methacrylate)                                                                   1.517      365                                           Poly(2-diethylaminoethyl methacrylate)                                                             1.5174     289                                           Natural rubber       1.519-1.52 200                                           Polyacrylonitrile    1.52                                                     Polymethacrylonitrile                                                                              1.52                                                     Polyisoprene         1.521      200                                           Polyacrylic acid     1.527      379                                           Poly(1-vinyl-2-pyrrolidone)                                                                        1.53       327                                           Cellulose            1.54       243-443                                       Polyvinyl chloride   1.54-1.55  354                                           Poly(2-bromoethyl methacrylate)                                                                    1.5426     325                                           Poly(N-allyl methacrylamide)                                                                       1.5476     433                                           Polyisopropyl methacrylate                                                                         1.552      354                                           Poly(p-isopropyl styrene)                                                                          1.554      360                                           Polychloroprene      1.554-1.558                                                                              253                                           Polybenzyl methacrylate                                                                            1.5680     327                                           Polyphenyl methacrylate                                                                            1.5706     383                                           Poly(oxy-2,6-dimethylphenylene)                                                                    1.575      482                                           Polyoxyethylene oxyterephthaloyl                                                                   1.5750     342                                           (amorphous)                                                                   Polyvinyl benzoate   1.5775     344                                           Poly(4-methoxy-2-methylstyrene)                                                                    1.5868     358                                           Poly(o-methylstyrene)                                                                              1.5874     409                                           Polystyrene           1.59-1.592                                                                              373                                           Poly(o-methoxystyrene)                                                                             1.5932     348                                           Poly(p-methoxystyrene)                                                                             1.5967     362                                           Polyvinylidene chloride                                                                            1.60-1.63  255                                           Poly(o-chlorostyrene)                                                                              1.6098     392                                           Poly(2,6-dichlorostyrene)                                                                          1.6248     440                                           Polyvinyl naphthalene                                                                              1.6818     432                                           Polyvinyl carbazole  1.683      423, 481                                      ______________________________________                                    

Among the above-mentioned polymers, those which have a relatively low Tgand excellent cushioning properties are particularly preferable, i.e.,polyvinyl acetate, polybutadiene, polyvinyl butyral, urethane acrylateresins.

Examples of plasticizers usable in the present invention includepolyhydric alcohols, phthalate plasticizers, aliphatic dibasic esterplasticizers, citrate plasticizers, epoxy plasticizers, and phosphateplasticizers.

Examples of preferable polyhydric alcohols are ethylene glycol,diethylene glycol, triethylene glycol, glycerin, trimethylolpropane,etc.

Examples of preferable phthalate plasticizers are dimethyl phthalate(DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), heptylnonylphthalate (HNP), di-2-ethylhexyl phthalate (DOP), di-n-octyl phthalate(DNOP), di-i-octyl phthalate (DCapP), phthalic acid (79 alkyl) (D79P),di-i-decyl phthalate (DIDP), ditridecyl phthalate (DTDP), dicyclohexylphthalate (DCHP), butyl benzyl phthalate (BDP), ethyl phthalyl ethylglycolate (EPEG), butyl phthalyl butyl glycolate (BPBG), etc.

Examples of preferable aliphatic dibasic ester plasticizers aredi-2-ethylhexyl adipate (DOA), adipic acid di(methylcyclohexyl),diisodecyl adipate (DIDA), di-n-hexyl azelate (DNHZ), di-2-ethylhexylazelate (DOZ), dibutyl sebacate (DBS), di-2-ethylhexyl sebacate (DOS),etc.

Examples of preferable citrate plasticizers are triethyl citrate (TEC),tributyl citrate (TBC), acetyl triethyl citrate (ATEC), acetyl tributylcitrate (ATBC), etc.

Examples of preferable epoxy plasticizers are epoxidized soybean oil(EPO), etc.

Examples of preferable phosphate plasticizers are tributyl phosphate(TBP), triphenyl phosphate (TPP), tricresyl phosphate (YCP),tripropylene glycol phosphate, etc.

The thickness of each cushioning layer is in the range of 1 μm to 1,000μm, preferably in the range of 20 μm to 100 μm. If the cushioning layeris excessively thin, the cushioning properties are inferior. If thecushioning layer is excessively thick, adverse effects are made on theoptical properties (haze, transmittance, etc.).

The amount of plasticizer contained in the binder is in the range of 0to 80%, preferably in the range of 10% to 50%. If the plasticizercontent is excessively low, the effect on the plasticity is low,whereas, an excessively high plasticizer content causes a lowering inthe strength of the resulting coating.

If the cushioning layer is a polymer layer comprising an adhesive mass,the polymer layer may be formed by coating an adhesive polymer on aglass substrate in the form of a solution. Alternatively, an adhesivepolymer in the form of a film may be laminated on a glass substrate.Either of the described methods is usable in the present invention.

Solution Coating Method

In this method, a solvent-type adhesive is dissolved in a solvent or thelike, and the resulting solution is coated on a glass substrate and thendried. Examples of adhesives usable in the present invention includerubber, acrylic and silicone adhesives.

Examples of rubber adhesives usable in the present invention are naturalrubber, styrene-butadiene rubber, polyisobutylene rubber, isoprenerubber, etc.

Examples of acrylic adhesives usable in the present invention arecopolymers containing 2-ethylhexyl acrylate as a principal monomer, andso forth.

Examples of silicone adhesives usable in the present invention aresilicone polymers containing rubber-like siloxane or resinous siloxaneas a principal component.

Examples of solvents usable for coating are toluene, Triclene, n-hexane,ethyl acetate, methyl ethyl ketone, etc.

Emulsion adhesives and hot-melt adhesives are also usable.

Film Laminating Method

It is possible to use a commercially available double-side adhesivewhich is formed in the shape of a carrier film from one adhesiveselected from among the above. The double-side adhesive is preferablycomprised exclusively of an adhesive, as shown in FIG. 2(a). Thedouble-side adhesive shown in FIG. 2(a) comprises an adhesive layerhaving protective films 22 attached to both sides thereof. In the caseof an adhesive cushioning layer wherein adhesive layers 21 are attachedto both sides of a carrier film 20, as shown in FIG. 2(b), the film mustbe made of polypropylene, polyvinyl chloride, etc. which causes no orsubstantially no polarization. If the carrier film is made of a materialwhich causes polarization, e.g., PET, striped irregularities areundesirably produced in the resulting duplicate.

In addition to the above-described polymers, ionizing radiation curingmaterials are also usable.

As ionizing radiation curing materials, electron radiation curing resinsand ultraviolet curing resins are useful. Electron radiation curingresins and ultraviolet curing resins are similar to each other in termsof the constituents except that the latter resins containphotopolymerization initiator and a sensitizer. Generally, it ispreferable to use an ionizing radiation curing material which containsas a principal component a polymer, oligomer or monomer having a radicalpolymerizable active group in its structure as a film-forming component.As a polymer or oligomer of this type, a commercially available materialsuch as urethane acrylate or polyester acrylate is applicable to thepresent invention. As a monomer, a commercially available ionizingradiation curing monomer, e.g., an acrylic acid or methacrylic acidderivative, is applicable to the present invention. The above-describedionizing radiation curing resin materials can be employed as ultravioletcuring resin materials by mixing them with a photopolymerizationinitiator, e.g., acetophenone, benzophenone, Michler's benzoylbenzoate,α-aminoxime ester, tetramethyl thiuram monosulfide, thioxanthone, etc.,and a photosensitizer, e.g., n-butylamine, triethylamine,tri-n-butylphosphine, etc.

As an ionizing radiation irradiation method, a prior art can be employedas it is. In the case of electron radiation irradiation, for example, anionizing radiation curing resin material can be cured by irradiating itwith electron radiation having an energy of 50 KeV to 1,000 KeV,preferably 100 KeV to 300 KeV, emitted from an electron radiationaccelerator selected from among a variety of accelerators, e.g., aCockcroft-Walton's accelerator, a van de Graaff accelerator, a resonancetransformer type accelerator, an insulating core transformer typeaccelerator, a linear accelerator, a dynamitron accelerator, ahigh-frequency accelerator, etc., at a dose rate of 0.1 Mrad. to 100Mrad., preferably 1 Mrad. to 10 Mrad. In the case of ultravioletirradiation, an ultraviolet curing resin material can be cured byirradiating it with ultraviolet radiation emitted from a light source,e.g., an extra-high pressure mercury lamp, a high-pressure mercury lamp,a carbon arc lamp, a xenon arc lamp, a metal halide lamp, etc., at adose rate of 0.1 mJ/cm² to 10,000 mJ/cm², preferably 10 mJ/cm² to 1,000mJ/cm².

The hologram duplicating apparatus of the present invention will bedescribed below with reference to FIG. 3.

As shown in FIG. 3, a duplicating photosensitive material film 21 isdelivered from a supply roller 22 and taken up by a take-up roller 23.An original plate layer 26 is placed on a vertically movable support 24.A contacting liquid is dropped on the original plate layer 26 from acontacting liquid dropping device 25, and the original plate layer 26 isthen-brought into close contact with the duplicating photosensitivematerial film 21 by raising the support 24. An excess of contactingliquid is removed by squeezing with a roller 27. Next, the contactingliquid is dropped on the recording film 21 from a contacting liquiddropping device 28, and the recording film 21 is then brought into closecontact with an AR coated ND layer 29. At this time also, an excess ofcontacting liquid is squeezed out by a roller or the like, and the NDlayer 29 is pressed so as to come in close contact with the recordingfilm 21 by a pressing device 32. If the ND layer 29 is so thick that itcannot satisfactorily be squeezed by a roller, the thickness of the NDlayer 29 is reduced to 0.1 mm to 1.5 mm. In addition, a polymericmaterial which causes no double refraction and is equal to thecontacting liquid in refractive index is employed for the ND layer 29,thereby making it flexible so that an excess of contacting liquid cansatisfactorily be squeezed out. Further, by providing the AR coated NDlayer 29 with a cushioning layer, vibration of the contacting liquid canbe suppressed during exposure for duplication.

A laser beam 30 that is conjugated with the original plate layer is madeincident on the duplicating system thus formed, thereby effectingexposure for duplication. Upon completion of the duplication, the ARcoated ND layer 29 is removed, and the recording film 21 is separatedfrom the duplicating system by processing the original plate layer. Theseparated recording film 21 enters a drying chamber 31 where it is driedto remove the contacting liquid therefrom. The dried film 21 iscollected onto the take-up roller 23. These steps are carried out as aseries of operations so that duplication is continuously performed. Theproductivity can be increased by providing a plurality of exposuresections and a plurality of drying sections.

EXAMPLES 1 to 3

The following solutions were each coated on an original plate glass byan applicator.

EXAMPLE 1

    ______________________________________                                        Gelatin (P3829: Nitta Gelatin)                                                                  100 parts by weight                                         Water              50 parts by weight                                         (solution at 50° C.)                                                   ______________________________________                                    

EXAMPLE 2

    ______________________________________                                        Gelatin (P3829: Nitta Gelatin)                                                                  50 parts by weight                                          Glycerin          40 parts by weight                                          Water             40 parts by weight                                          (solution at 50° C.)                                                   ______________________________________                                    

EXAMPLE 3

    ______________________________________                                        Gelatin (P3829: Nitta Gelatin)                                                                   50 parts by weight                                         Gelatin (Type U: Nitta Gelatin)                                                                  10 parts by weight                                         Glycerin           40 parts by weight                                         Water              40 parts by weight                                         (solution at 50° C.)                                                   ______________________________________                                    

After being coated, each solution was cooled to 0° C. to form a coatingfilm of 50 μm in thickness. Then, the film was dried on heating for 1hour at 100° C., thereby forming a cushioning layer.

It should be noted that the solution in [Example 2] was also spin-coatedon an UV ozone-treated glass substrate at 250 rpm, thereby forming acushioning layer.

EXAMPLE 4

    ______________________________________                                        Agar        100 parts by weight                                               Water        50 parts by weight                                               (solution at 90° C.)                                                   ______________________________________                                    

After being coated, the solution was cooled to 0° C. to form a coatingfilm of 50 μm in thickness, thereby producing a cushioning layer (4).

EXAMPLES 5 and 6

The following solutions were each coated on an original plate glass byan applicator.

EXAMPLE 5

    ______________________________________                                        Polyvinyl acetate (Gosenyl PV-500: Nippon                                                           100     parts by weight                                 Synthetic Chemical Industry Co., Ltd.)                                        Di-2-ethylhexyl phthalate (DOP: Daihachi                                                            30      parts by weight                                 Kagaku)                                                                       Methyl ethyl ketone   150     parts by weight                                 Toluene               50      parts by weight                                 ______________________________________                                    

EXAMPLE 6

    ______________________________________                                        Polyvinyl butyral (Eslec BX-1: Sekisui Chemical                                                      100    parts by weight                                 Co., Ltd.)                                                                    Di-2-ethylhexyl phthalate (DOP: Daihachi                                                             30     parts by weight                                 Kagaku)                                                                       Methyl ethyl ketone    150    parts by weight                                 Toluene                50     parts by weight                                 ______________________________________                                    

After being coated, each solution was dried on heating for 5 minutes at100° C., thereby forming a coating film of 50 μm in thickness. Thus, acushioning layer was produced on each original plate glass.

EXAMPLE 7

The following solution was spin-coated on an original plate glass.

    ______________________________________                                        Coating type adhesive:                                                        ______________________________________                                        Acrylic copolymer                                                                             100        parts by weight                                    Xylene resin    10         parts by weight                                    Isophorone di-isocyanate                                                                      1          part by weight                                     Ethyl acetate   150        parts by weight                                    ______________________________________                                    

After being coated, the solution was dried on heating for 5 minutes at100° C., thereby forming a coating film of 50 μm in thickness. Thus, acushioning layer (7) was produced.

EXAMPLE 8

A double-side adhesive film (Neomask: Nitto Electric Industrial Co.,Ltd.) was stuck on an original plate glass by using a rubber roller,thereby producing a cushioning layer (8).

EXAMPLE 9

An ultraviolet curing resin material (Aronix UV-3033: Toa Gosei ChemicalIndustry Co., Ltd.) was coated to a thickness of 50 μm on an originalplate glass and then irradiated with ultraviolet radiation, therebyproducing a cushioning layer (9).

EXAMPLE 10

The following solution was spin-coated on an original plate glass.

    ______________________________________                                        Urethane acrylate (UV-3000B: Nippon Synthetic                                                        100    parts by weight                                 Chemical Industry Co., Ltd.)                                                  Acrylic monomer (Aronix M-101: Toa Gosei                                                             100    parts by weight                                 Chemical Industry Co., Ltd.)                                                  Dipentaerythritol pentaacrylate (Sartomer 399:                                                       20     parts by weight                                 Sartomer)                                                                     ______________________________________                                    

Then, the coated solution was irradiated with electron radiation tothereby produce a cushioning layer of 50 μm in thickness.

EXAMPLES 11 and 12

In Examples 11 and 12, an UV cured urethane acrylate layer was producedby mixing an initiator (Irgacure 184: Ciba-Geigy Ltd.; 3 to 5 wt %) withthe material.

EXAMPLE 11

SC-3120 (The inktec)+Irgacure

EXAMPLE 12

    ______________________________________                                        N-vinyl-2-pyrrolidone (Toa Gosei Chemical                                                            50     parts by weight                                 Industry Co., Ltd.)                                                           Aronix M-5600 (Toa Gosei Chemical Industry                                                           50     parts by weight                                 Co., Ltd.)                                                                    UV-3000B (Nippon Synthetic Chemical Industry                                                         100    parts by weight                                 Co., Ltd.)                                                                    HK-20 (Toa Gosei Chemical Industry Co., Ltd.)                                                        2      parts by weight                                 ______________________________________                                    

In Examples 11 and 12, the glass (or PMMA) laminating method wasemployed. That is, the solution was heated to a temperature of 50° C. to80° C. so as to have a viscosity of not higher than 1,000 cps anddropped on one end of a glass substrate or an acrylic resin materialcoated with a primer (Chemlock 607 diluted 1:10 with methanol) andheated to the same temperature. Then, a heated glass, which was coatedwith a parting agent (Moldspat MR-K681: Asahi Glass Company Ltd.), wasplaced thereon and pressed so that the solution gradually spread. AfterUV exposure, the upper glass was separated.

Rolograms was produced by using the original plates prepared in Examples1 to 12. As a result, it was possible to produce excellent duplicateholograms which had minimal defects (Table 1). It should be noted thatthe results shown in Table 1 were obtained when Omnidex 352 (Du PontCo., Ltd.) was employed as a duplicating photosensitive material.

In contrast, when duplication was carried out without providing acushioning layer, a large number of defects due to dust were observed.

                  TABLE 1                                                         ______________________________________                                        Examples                                                                             Cushioning layer                                                                           Coating method                                                                            Number of defects *                           ______________________________________                                        1      gelatin      applicator  25                                            2      gelatin      applicator  4.3                                           2      gelatin      spin coating                                                                              1.5                                           3      gelatin      applicator  1.9                                           4      agar         applicator  6.8                                           5      polyvinyl    applicator  30                                                   acetate                                                                6      polyvinyl    applicator  30                                                   butyral                                                                7      adhesive     spin coating                                                                              20                                            8      adhesive     laminating  10                                            9      ionizing radiation                                                                         applicator  5.6                                                  cured film                                                             10     ionizing radiation                                                                         spin coating                                                                              5.8                                                  cured film                                                             11     ionizing radiation                                                                         glass       1.0                                                  cured film   laminate                                                  12     ionizing radiation                                                                         glass       0.5                                                  cured film   laminate                                                         no cushioning layer      about 400                                     ______________________________________                                         Note: * Number of defects (mean value) per 5 in. × 5 in.           

Thus, since a flexible ND glass or sheet is provided or a cushioninglayer is provided on the side of an ND glass which is closer to anoptical contacting liquid layer, pressure is uniformly transmitted tothe contacting liquid so that the contacting liquid layer can be madeuniform and thin in thickness, thereby preventing undesirable flow ofthe contacting liquid during exposure. Thus, it is possible to producean excellent duplicate hologram. It is also possible to increase theproductivity of duplication of the hologram by feeding the recordingfilm continuously. In addition, a cushioning layer is provided on theinner side of an AR coated ND glass or the upper side of aphotosensitive material film, and another cushioning layer is providedon the side of an original plate protecting glass which is closer to anoptical contacting liquid layer or on the lower side of thephotosensitive material film. With this arrangement, if dust is mixedin, it is held inside the relevant cushioning layer. Thus, it ispossible to prevent undesirable flow of the contacting liquid andlifting of the film by foreign substances. Accordingly, duplication ofthe hologram can be effected without any hindrance.

Evaluation of the properties of the above-described cushioning layerswill be explained below.

The properties required for the cushioning layers in terms of theremoval of defects due to foreign substances are (1) capability ofeffectively burying foreign substances therein when a duplicatingphotosensitive film is brought into close contact with it, and (2) platewear resistance with which it can be repeatedly used for duplication.Mechanical properties corresponding to these essential properties are(1) "softness" adequate to bury foreign particles in the cushioninglayer when such particles are held between the same and the duplicatingphotosensitive film, and (2) "elasticity" with which depressions formedby burying foreign particles are restored every time the duplicatingphotosensitive film is separated from the cushioning layer after eachexposure process, and with which no undulation occurs in the surface ofthe cushioning layer when it is squeezed with a roller when theduplicating photosensitive film is brought into close contact with thecushioning layer. To express quantitatively mechanical propertiesadequate to attain the desired purpose, we devised [1] stylusforce-displacement measuring test and [2] pencil scratch test asevaluation testing methods for the above-described two properties, andcarried out these evaluation testing methods on several different kindsof cushioning layer. Further, these cushioning layers were actuallyrepeatedly used for hologram duplication to examine the correlationbetween the incidence of defects and the evaluation test results. Thetwo evaluation testing methods are as follows:

[1] Stylus force-displacement measurement

(Purpose) The purpose of this test is to express quantitatively"softness" of a polymer film of several ten μm in thickness coated on aglass substrate.

(Method) A surface configuration measuring device for large-sizedsubstrates, Dektak-16000 (ULVAC) is employed. A part of the sample filmsurface is separated to expose the surface of the glass substrate. Witha predetermined load (stylus force) applied to a diamond stylus having atip diameter of 12.5 μm, the step portion that is defined between theglass substrate and the polymer film at the separated portion islinearly scanned with the diamond stylus. Thus, a difference betweenvertical coordinates of the stylus, that is, a film thickness, is readat predetermined coordinates (in the scanning direction) of the exposedportion of the glass substrate and the coating film portion. With thestylus force step wisely varied in the range of 1 mgf to 30 mgf, thesame measurement is repeated at the same position. The film thickness isplotted against the stylus force and approximated by a straight line, asshown in FIG. 4. The slope (absolute value) of the straight lineobtained represents the displacement (μm) of the film surface per unitstylus force (mgf).

[2] Pencil scratch test

[Purpose] The purpose of this test is to obtain an index that representselasticity (resilience) of a polymer film of several ten μm in thicknesscoated on a glass substrate.

(Method) A device (pencil scratch tester) defined by JIS K 5401 andpencils (6H to 5B) defined by JIS S6006 are employed. The testing methodis carried out according to JIS K 5400 6.14 "Pencil scratch test". Inthe present invention, however, the load that is applied to the pencilis set at 50 g.

The stylus force-displacement measurement and pencil scratch test werecarried out on the following five different kinds of cushioning layer.The thickness of the cushioning layers were in the range of 20 μm to 50μm.

(Cushioning layer 1)

A solution of the following composition was spin-coated on a glasssubstrate and then dried by allowing it to stand for 1 day at roomtemperature.

    ______________________________________                                        Gelatin (Collotype-I: Nitta Gelatin)                                                             10 parts by weight                                         Glycerin (Junsei Kagaku)                                                                         40 parts by weight                                         Water              50 parts by weight                                         ______________________________________                                    

(Cushioning layer 2)

A solution of the following composition was dropped on one end of aglass substrate, and a glass (cover glass) coated with a parting agent(Moldspat MR-K681: Asahi Glass Company Ltd.) was placed thereon andpressed so that the solution spread uniformly. After curing byirradiation with ultraviolet radiation, the cover glass was separated.

    ______________________________________                                        Soft coat (SC-3120: The Inktec)                                                                      100    parts by weight                                 Photopolymerization initiator (Irgacure 184: Ciba-                                                   4      parts by weight                                 Geigy Ltd.)                                                                   ______________________________________                                    

(Cushioning layer 3)

The following solution was spin-coated on a glass substrate, and afterbeing irradiated with ultraviolet radiation, it was dried on heating(for 2 hours at 120° C).

Photosensitive material for holography

(Omnidex 352: Du Pont Co., Ltd.)

(Cushioning layer 4)

With a solution of the following composition used, the same procedure asin the case of the cushioning layer 2 was carried out.

    ______________________________________                                        Monomer                25    parts by weight                                  (Aronix M-150: Toa Gosei Chemical                                             Industry Co., Ltd.)                                                           Monomer                25    parts by weight                                  (Aronix M-5600: Toa Gosei Chemical                                            Industry Co., Ltd.)                                                           Urethane acrylate      50    parts by weight                                  (UV-3000B: Nippon Synthetic Chemical                                          Industry Co., Ltd.)                                                           Monomer                1     part by weight                                   (HK-2: Toa Gosei Chemical Industry Co., Ltd.)                                 Photopolymerization initiator                                                                        4     parts by weight                                  (Irgacure 184: Ciba-Geigy Ltd.)                                               ______________________________________                                    

(Cushioning layer 5)

The following solution was coated on a glass substrate by an applicatorand thereafter cured by irradiation with electron radiation.

Urethane acrylate

(PR-202: Mitsubishi Chemical Industries, Ltd.)

FIG. 4 is a graph showing the results of the stylus force-displacementtest carried out on the above-described five different kinds ofcushioning layer. It should be noted that the axis of ordinates in thegraph represents not the film thickness but the displacement of the filmthickness. In addition, numerals in the graph represent the slopes ofthe straight lines.

Next, the pencil scratch test was carried out on the same samples. Theresults of the test are shown in Table 2 below. It should be noted thata higher hardness symbol represents a higher pencil scratch value, andthe results expressed by inequality signs each show that the hardness ofthe cushioning layer is outside the hardness range of the pencil used.

                  TABLE 2                                                         ______________________________________                                        (result of pencil scratch test                                                on each cushioning layer)                                                     Cushioning layer                                                                            Pencil scratch value                                            ______________________________________                                        1             <5B                                                             2             >6H                                                             3             <5B                                                             4             >6H                                                             5             <5B                                                             ______________________________________                                    

The cushioning layers (1 to 5) on the respective glass substrates wereeach-repeatedly used for hologram duplication 10 times by using anapparatus as shown in FIG. 3, with the glass substrate brought intoclose contact with an original plate unit through an optical contactingliquid, and with the cushioning layer brought into close contact with aduplicating film through an optical contacting liquid, to examine anumber of defects (per 5 in²) generated in a hologram produced by eachduplication process and the condition of undulation of the cushioninglayer surface. The results of the measurement are shown in Table 3below, together with the results of the stylus force-displacementmeasurement and pencil scratch test.

                  TABLE 3                                                         ______________________________________                                        (relationship between the number of times of repeated                         duplication, the slope of the stylus force-                                   displacement straight line, the pencil scratch value,                         the number of defects and the condition of undulation)                              Slope of                 Number of                                            stylus                   depression-                                          force-            Number of                                                                            shaped                                         Cush- displacement                                                                            Pencil  times of                                                                             defects                                        ioning                                                                              straight line                                                                           scratch duplica-                                                                             1/(5 × 5                                 layer (μm/mgf)                                                                             value   tion   inch.sup.2)*)                                                                         Undulation                             ______________________________________                                        1     0.359     <5B     1       6  (5) very large                                                     10      37 (24)                                       2     0.089     >6H     1       5  (5) medium                                                         10      8  (8)                                        3     0.061     <5B     1       5  (4) large                                                          10      8  (4)                                        4     0.039     >6H     1       2  (2) small                                                          10      8  (8)                                        5     0.003     <5B     1       58     unexamined                                                            (uncounted)                                    No    --        --      1      more than                                                                             --                                     layer                          400                                                                           (uncounted)                                    ______________________________________                                         Note:                                                                         *) numerals in the parentheses each represent the number of                   depressionshaped defects containing foreign particles among the total         number of defects.                                                       

From the above examination, the following conclusion may be drawn:

In the four cushioning layers (1 to 4) where the slope of the stylusforce-displacement straight line exceeds 0.003 μm/mgf, the number ofdefects occurring during the first duplication was small, that is,substantially equal (not larger than 6) to each other, whereas, in thecushioning layer 5 having a smaller slope than those of the cushioninglayers 1 to 4, a number of defects which was about 10 times that of thecushioning layers 1 to 4 occurred. Thus, the cushioning layer 5 cannotbe put to practical use. Accordingly, it will be understood that thecushioning layer in the present invention must have a stylusforce-displacement straight line slope of at least 0.003 μm/mgf.

In the cushioning layers 1 and 3 whose pencil scratch values are lowerthan 5B, the ratio of depression-shaped defects where no foreignparticle can be found becomes higher as the cushioning layers 1 and 3are repeatedly used. On the other hand, in the cushioning layers 2 and 4whose pencil scratch values are higher than 6H, the above-describedratio is lower than that of the cushioning layers 1 and 3. In addition,there is a difference in terms of undulation between the cushioninglayers 1 and 3 on the one hand and the cushioning layers 2 and 4 on theother. That is, if the pencil scratch value is lower than 6H, undulationmarkedly occurs during the repeated use. Therefore, such a cushioninglayer cannot withstand repeated use.

If the center of a depression-shaped defect in a hologram which isproduced by duplication without using a cushioning layer is observed byusing an optical microscope (MHL100: Olympus Optical Co., Ltd.) at amagnification of 50 to 200 by the reflected- or incident-lightillumination dark-field observation method, it is revealed that theobserved portion contains holographical record of a foreign substanceitself (smaller than about 10 μm) or a distorted portion (acrater-shaped dark portion of several 10 μm to about 200 μm in diameter)of the duplicating film where it is locally pressed by a foreignsubstance. If a portion of a hologram duplicatively produced by usingthe cushioning layer 5 where no depression-shaped defect is recognizedis observed by the same method as the above, it is revealed that theobserved portion contains the record of a foreign substance or adistortion of the surface region of the cushioning layer due to aforeign substance in the same way as the above. FIG. 5(a) is aphotograph of a reconstructed image of a foreign substance itselfobserved by the above-described method (magnification: 200; film: FUJIFP-3000B SUPER, ISO3200; and exposure time: 12.25 sec.). FIG. 5(b) is aphotograph of a reconstructed image of a portion of a cushioning layerthat is distorted by a foreign substance on the film (magnification:200; film: the same as the above; and exposure time: 13.37 sec.). Ifduplication is carried out without employing a cushioning layer, such aforeign substance would press the duplicating film, causing thereconstructed image to have a depression-shaped defect of the order ofseveral hundred μm to several mm in diameter. However, when a cushioninglayer is employed, even if a foreign substance is present, it iseffectively buried in the cushioning layer so as not to press the film.It is therefore possible to prevent occurrence of a depression-shapeddefect. However, in a hologram produced by duplication using acushioning layer, a portion where no depression-shaped defect is presentcontains the record of traces of foreign substances as microscopicallyrecognized by observation using an optical microscope, as shown in FIGS.5(a) and 5(b).

Thus, by providing a cushioning layer, which contains as a principalcomponent a polymer of high elasticity having a slope greater than 0.003μm/mgf in the stylus force-displacement measurement, on the side of ananti-reflection coated glass, an ND glass or an original plateprotecting glass which is closer to the photosensitive material film, oron the side of the film which is closer to the glass, even if a foreignsubstance enters the area between the glass and the film, it iseffectively buried in the cushioning layer, thereby preventingundesirable flow of the contacting liquid and lifting of the film. Thus,it is possible to produce a hologram capable of forming a reconstructedimage where no defect is recognized by visual observation, although thehologram contains the record of microscopic traces of foreign substanceswhich can be recognized with an optical microscope.

The following is a description of examples in which the opticalcontacting liquid contains a surface active agent.

FIG. 6 shows an example of a hologram that employs a flexible ND glassprovided with an anti-reflection (AR) coating. On the AR coated ND glass1, an original plate supporting glass 3 is placed in close contact withit through an optical contacting liquid 2. An original plate film 41 issupported by the supporting glass 3, and an original plate protectingglass 6 is bonded to the original plate film 4 with an optical adhesive5, thereby forming an original plate unit. On the original plate unit, aduplicating photosensitive material film 8 is placed with an opticalcontacting liquid 7 interposed therebetween, and an optical contactingliquid 9 and an AR coated ND glass 10 are successively stacked up on thefilm 8, thereby forming a duplicating unit. The AR coated ND glass 10 ismade flexible by reducing the thickness thereof to the range of 0.1 mmto 1.5 mm. When the AR coated ND glass 10 is pressed in close contactwith the duplicating photosensitive material film 8 with the opticalcontacting liquid 9 interposed therebetween, since the glass 10 isflexible, the pressure is uniformly transmitted to the opticalcontacting liquid 9, so that the optical contacting liquid 9 can be madeuniform and extremely thin in thickness.

In the present invention, the optical contacting liquid that is employedto form each layer is allowed to contain a cationic, anionic, ampholyticor nonionic surface active agent, thereby improving the wettability withrespect to the base material and thus preventing trapping of air. Forinstance, if an optical contacting liquid alone is dropped on a basematerial 40, it becomes spherical, as shown in FIG. 7(a), because of thesurface tension thereof. In contrast, if a surface active agent is addedto the optical contacting liquid, the liquid spreads over the basematerial 40, as shown in FIG. 7(b), because of the improvement in thewettability with respect to the base material 40. If the opticalcontacting liquid alone is dropped on the base material 40 and spreadthereover, air is trapped in the optical contacting liquid as airbubbles, as shown in FIG. 8(a), whereas, if the optical contactingliquid, which contains a surface active agent, is spread over the basematerial 40, it can be uniformly coated without trapping of air, asshown in FIG. 8(b).

Thus, if exposure is carried out with the original plate unit and theduplicating unit brought into close contact each other using an opticalcontacting liquid containing a surface active agent, since the opticalcontacting liquid is free from trapping of air and can be made uniformand extremely thin in thickness, the hologram image can be duplicatedexcellently. That is, in a case where the original plate is a reflectionhologram, when a laser beam is made incident from the duplicating unitside, diffracted light from the original plate and the incident laserlight interfere with each other in the duplicating photosensitivematerial film 8. Thus, the hologram image can be duplicatedsatisfactorily.

It should be noted that if a surface active agent having antistaticproperties is used, it is also possible to prevent trapping of air dueto static electrification. If a surface active agent having anti-foamingproperties is used, it is also possible to prevent foaming due tomechanical transport or stirring during the supply of the opticalcontacting liquid.

Surface active agents which are usable in the present invention will beexplained below.

Examples of cationic surface active agents usable in the presentinvention include primary amine salts, secondary amine salts, tertiaryamine salts, quaternary ammonium salts, etc.

Examples of anionic surface active agents usable in the presentinvention include carboxylates, sulfates, sulfonates, phosphates, etc.

Examples of ampholytic surface active agents usable in the presentinvention include amino acid type ampholytic surface active agents,betaine type ampholytic surface active agents, etc.

Examples of nonionic surface active agents usable in the presentinvention include various kinds of alcohol, polyethylene glycol typenonionic surface active agents, polyhydric alcohol type nonionic surfaceactive agents, etc.

Surface active agents are used for a variety of purposes, for example,wetting agents, penetrating agents, foaming agents, anti-foaming agents,emulsifying agents, antistatic agents, etc. In the present invention,wetting properties, which are concerned with wettability, anti-foamingproperties for suppressing foaming, and antistatic properties forpreventing static electrification are important factors.

As a surface active agent which is excellent in wetting properties, asulfonate type surface active agent, a sulfate type surface activeagent, or a nonionic surface active agent having a large HLB value issuitable for the present invention.

As a surface active agent which is excellent in anti-foaming properties,a lower alcohol or a nonionic surface active agent having a low HLBvalue is suitable for the present invention.

Examples of surface active agents which are excellent in antistaticproperties and suitable for the present invention include anionic,cationic and ampholytic surface active agents.

As an optical contacting liquid, it is preferable to use a liquid havinga refractive index close to that of a base material used.

The refractive indices of main compounds, which are usable as an opticalcontacting liquid, are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Compounds        Refractive index                                             ______________________________________                                        Acrylaldehyde    1.39975                                                      Acetylacetone    .45178                                                       Acetaldehyde     .33157                                                       Acetonitrile     .34596                                                       Acetophenone     .53427                                                       Acetone          .35886                                                       Anisole          .51503                                                       Aniline          .58629                                                       Allyl alcohol    .41152                                                       Isooctane        .3916                                                        Isoquinoline     .62233                                                       Isobutyl alcohol .39396                                                       Indene           .5768                                                        Ethanol          .36232                                                       Ethylbenzene     .4994                                                        Ethylene glycol  .42743                                                       Ethylenediamine  .45400                                                       Benzoyl chloride .55369                                                       Octane           .39755                                                       Formic acid      .37137                                                       Ethyl formate    .35985                                                       o-xylene         .50777                                                       m-xylene         .49962                                                       p-xylene         .49734                                                       Valeric acid     .40433                                                       Quinoline        .62450                                                       Glycerin         .4746                                                        1-chloronaphthalene                                                                            .63321                                                       Chlorobenzene    .52479                                                       Chloroform       .44671                                                       Acetic acid      .37182                                                       Ethyl acetate    .37257                                                       Diethylamine     .38730                                                       Diethyl ether    .3542                                                        1,1-diethoxyethane                                                                             .38193                                                       Carbon tetrachloride                                                                           .46072                                                       Dioxane          .4224                                                        Cyclohexanol     .46055                                                       Cyclohexanone    .4507                                                        Cyclohexane      .42680                                                       Cyclohexene      .4465                                                        Cyclopentane     .40609                                                       1,2-dichloroethane                                                                             .44439                                                       Dichloromethane  .42721                                                       Dibromomethane   .54463                                                       Ethyl bromide    .42406                                                       Styrene          --                                                           Thiophenol       .58613                                                       Thiophene        .52853                                                       cis-decalin      .4810                                                        trans-decalin    .4695                                                        Decane           1.41203                                                      1-decene         .4215                                                        Tetrachloroethylene                                                                            .50547                                                       Tetrahydrofuran  .404                                                         Triethylamine    .40032                                                       Trichloroacetaldehyde                                                                          .45572                                                       Trichloronitromethane                                                                          .46075                                                       o-toluidine      .57276                                                       Toluene          .49782                                                       Nicotine         .52392                                                       Nitroethane      .39007                                                       Nitrobenzene     .55319                                                       Nitromethane     .38133                                                       Carbon disulfide .62801                                                       (+)-a-pinene     .46634                                                       Pyridine         .50919                                                       Pyrrole          .50347                                                       Phenylhydrazine  .60813                                                       Phenol           .54247                                                       Butadiene        .422                                                         1-butanol        .39931                                                       2-butanol        .39743                                                       t-butyl alcohol  .38779                                                       Butyraldehyde    .38433                                                       Furan            --                                                           Furfural         .52608                                                       1-propanol       .38543                                                       2-propanol       .38126                                                       Propionic acid   .38659                                                       1-bromonaphthalene                                                                             .65876                                                       Bromobenzene     .55977                                                       Bromoform        .5890                                                        Hexane           .37536                                                       2-hexane         .39889                                                       Heptane          .38777                                                       Benzylamine      .54406                                                       Benzaldehyde     .54638                                                       Benzene          .47439                                                       Benzonitrile     .52570                                                       1-pentanol       .41173                                                       Pentane          .35801                                                       Formamide        .44530                                                       Mesitylene       .49804                                                       Methanol         .33001                                                       Methylal         .35344                                                       Methylcyclohexane                                                                              .42531                                                       2-methylpyridine .499                                                         Methyl iodide    .52973                                                       Iodobenzene      .62145                                                       Butyric acid     .39789                                                       Diethyl sulfide  .43055                                                       ______________________________________                                    

It is also possible to use Exxol DSP (refractive index: 1.405), ExxolD30 (1.437), Exxol D40 (1.445), Exxol D100 (1.445), Isoper E (1.404),Isoper G (1.417), Isoper H (1.424), Isoper L (1.427), and Isoper M(1.436), which are available from Exxon Kagaku, and Series AA (1.400 to1.458), Series A (1.460 to 1.640), and Series B (1.642 to 1.700), whichare available from Cargel.

In addition, a desired refractive index can be obtained by properlymixing together a plurality of compounds selected from among thosedescribed above.

EXAMPLE 13

An optical contacting liquid having the following composition was used.

    ______________________________________                                        Xylene               95    parts by weight                                    Nonionic surface active agent                                                                      5     parts by weight                                    (Emulgen 903: Kao Corporation)                                                ______________________________________                                    

EXAMPLE 14

An optical contacting liquid having the following composition was used.

    ______________________________________                                        Isoper L (Exxon Kagaku)                                                                              40    parts by weight                                  Series A (Cargel)      43    parts by weight                                  Nonionic surface active agent                                                                        3     parts by weight                                  (Leodole tw-S320: Kao Corporation)                                            Ampholytic surface active agent                                                                      1     part by weight                                   (Anon BDF: Nippon Oils & Fats Co., Ltd.)                                      ______________________________________                                    

When the optical contacting liquids of Examples 13 and 14 were used,there were substantially no defects due to trapping of air duringduplication.

Thus, by adding a surface active agent to the optical contacting liquid,mingling of air is prevented.

Accordingly, excellent duplication can be effected. If a surface activeagent having antistatic properties is used, it is possible to preventtrapping of air due to static electrification. If a surface active agenthaving anti-foaming properties is used, it is also possible to preventfoaming due to mechanical transport or stirring during the supply of theoptical contacting liquid.

The following is a description of examples in which an opticalcontacting liquid which is less fluidic and has a high viscosity of 100cps to 10,000 cps is used as a material serving as both a cushioninglayer and a contacting liquid in the formation of each layer in thelayer configuration shown in FIG. 6. Examples of such optical contactingliquids include liquid oligomers, polymer solutions, etc.

Examples of liquid oligomers usable in the present invention includeliquid polyurethane, liquid polyester, liquid polybutadiene, liquidpolyisoprene, etc.

As a polymer solution, it is possible to use one in which a polymer isdissolved at a concentration suitable for attaining the above-describedviscosity. In this solution, the polymer serves as a thickening agent.Various combinations of a polymer and a solvent may be used. It is,however, necessary to select a solvent which causes no damage to theoriginal plate and the duplicating film. It is also possible to add asurface active agent to the solution in order to prevent trapping ofair.

Thus, since the optical contacting liquid is free from trapping of airand made uniform and extremely thin in thickness, the hologram image canbe duplicated excellently. That is, in a case where the original plateis a reflection hologram, when a laser beam is made incident from theduplicating unit side, diffracted light from the original plate and theincident laser light interfere with each other in the duplicatingphotosensitive material film 8. Thus, the hologram image can beduplicated satisfactorily.

When the optical contacting liquid is a liquid substance comprising anionizing radiation curing polymer, monomer or the like, it may bepolymerized through a curing reaction caused by irradiation withionizing radiation during or after the duplication process, therebymaking it separable from the recording film.

EXAMPLE 15

As an optical contacting liquid, the following solution was used.

Liquid polybutadiene

Viscosity 200 cps

EXAMPLE 16

As an optical contacting liquid, the following solution was used.

    ______________________________________                                        Anisole                70    parts by weight                                  Polyvinyl acetate      30    parts by weight                                  (Nippon Synthetic Chemical Industry Co., Ltd.)                                Viscosity 1,000 cps                                                           ______________________________________                                    

With the optical contacting liquids of Examples 15 and 16, it waspossible to produce holograms having minimal defects.

EXAMPLE 17

As an optical contacting liquid, the following solution was used.

    ______________________________________                                        Urethane acrylate      95    parts by weight                                  (PR-202: Mitsubishi Chemical Industries, Ltd.)                                Photopolymerization initiator                                                                        5     parts by weight                                  (Irgacure 184: Ciba-Geigy Ltd.)                                               Viscosity 300 cps                                                             ______________________________________                                    

EXAMPLE 18

As an optical contacting liquid, the following solution was used.

    ______________________________________                                        Urethane acrylate      80    parts by weight                                  (PR-202: Mitsubishi Chemical Industries, Ltd.)                                Acrylic monomer        15    parts by weight                                  (Blemmer GLM: Nippon Oils & Fats Co., Ltd.)                                   Photopolymerization initiator                                                                        5     parts by weight                                  (Irgacure 184: Ciba-Geigy Ltd.)                                               Viscosity 4,000 cps                                                           ______________________________________                                    

With the optical contacting liquids of Examples 17 and 18, it waspossible to produce holograms having minimal defects. When ultravioletradiation was applied to the optical contacting liquids, they became setand were each capable of being removed from the film with ease.

Thus, a high-viscosity optical contacting liquid, which is less fluidic,can be used as a material that functions as both an optical contactingliquid and a cushioning layer for a flexible ND glass or sheet or an NDglass.

The following is a description of examples in which the AR coated NDglass 10 shown in FIG. 6 is made flexible.

In FIG. 6, the AR coated ND glass 10 is reduced in thickness to therange of 0.1 mm to 1.5 mm so as to become flexible. When the AR coatedND glass 10 is pressed in close contact with the duplicatingphotosensitive material film 8 with the optical contacting liquid 9interposed therebetween, since the glass 10 is flexible, the pressure isuniformly transmitted to the optical contacting liquid 9, so that thecontacting liquid 9 can be made uniform and extremely thin in thickness.When exposure is carried out in this state, since the optical contactingliquid is extremely thin, there is no undesirable flow of the liquid.That is, in a case where the original plate is a reflection hologram,when a laser beam is made incident from the duplicating unit side,diffracted light from the original plate and the incident laser lightinterfere with each other in the duplicating photosensitive materialfilm 8. Thus, the hologram image can be duplicated excellently.

FIG. 9 shows an example in which a flexible sheet 11 made of a polymericmaterial that satisfies the required optical conditions is provided inplace of the thin AR coated ND glass in FIG. 6. As the sheet 11 made ofa polymeric material, a sheet that causes no double refraction and hasbeen subjected to anti-reflection treatment and that is equal to theoptical contacting liquid in refractive index is used. Since the sheet11 itself is flexible, when pressure is applied thereto, the opticalcontacting liquid can be made uniform and extremely thin in thickness,and no undesirable flow of the optical contacting liquid occurs duringexposure, in the same way as in the case of FIG. 6. Accordingly, thehologram image can be duplicated excellently.

FIG. 10 shows an example in which a cushioning layer 12 is provided onthe inner side of a rigid AR coated ND glass 13. By virtue of thepresence of the cushioning layer 12, force acts uniformly on the opticalcontacting liquid, so that the optical contacting liquid can be madeuniform and thin in thickness in the same way as in the case of FIG. 1.Accordingly, no undesirable flow of the optical contacting liquid occursduring exposure, and it is possible to duplicate the hologram imageexcellently.

Thus, a flexible ND glass or sheet is provided, or a cushioning layer isprovided on the side of an ND glass which is closer to an opticalcontacting liquid, thereby allowing pressure to be uniformly transmittedto the contacting liquid so that the contacting liquid can be madeuniform and thin in thickness. Thus, it is possible to eliminateundesirable flow of the contacting liquid during exposure and henceproduce an excellent hologram by duplication. It is also possible toincrease the productivity of the hologram duplication by feeding therecording film continuously.

Next, a method of duplicating a hologram by using a spacer will beexplained with reference to FIGS. 11 to 16.

Referring to FIG. 11, a rigid spacer 53 is disposed on the periphery ofa photosensitive material 52 supported by a substrate 51, and the spacethat is defined by the spacer 53 is filled with an optical contactingliquid 54. Then, a substrate 55 for supporting a transmission hologramoriginal plate 56 is brought into close contact with the spacer 53 andthe optical contacting liquid 54 from thereabove. On the original plate56 are successively stacked up an ND glass 57 for damping the backreflection component and a substrate 58 provided with an anti-reflectioncoating in order to prevent surface reflection. Although the opticalcontacting liquid 54 is a syrupy liquid, the substrate 55 is broughtinto contact with the spacer 53 by the pressure applied from above it,so that the gap between the photosensitive material 52 and the substrate55 is maintained at a predetermined level. As a result, the thickness ofthe optical contacting liquid 54 is maintained at a predetermined level.By virtue of the presence of the spacer 53, the thickness of the opticalcontacting liquid 54 can be made uniform within a short time without theneed to apply a very high pressure.

As to the spacer 53, either a circular spacer or a plurality of dividedspacers may be provided on the periphery of the photosensitive material52. If glass or plastic beads having the same refractive index as thatof the optical contacting liquid 54 are dispersed in the opticalcontacting liquid 54, it is possible to maintain a predetermined gapequal to the diameter of the beads simply by coating the dispersion onthe upper side of the photosensitive material 52 and pressing thesubstrate 55.

If reconstruction light is applied from the upper side with apredetermined gap maintained between the photosensitive material 52 andthe substrate 55 as described above, the reconstruction light and thediffracted light from the original plate 56 interfere with each other inthe photosensitive material 52. Thus, a hologram image of the originalplate 56 can be duplicated efficiently without undesirable flow of theoptical contacting liquid 54.

FIG. 12 shows an embodiment in which the spacer 53 is disposed betweenthe original plate 56 and the ND glass 57. In this embodiment, thesubstrate 55 and the original plate 56 are successively stacked up onthe photosensitive material 52 supported by the substrate 51, and thespacer 53 is disposed on the original plate 56. Then, the space definedby the spacer 53 is filled with the optical contacting liquid 54, andthe ND glass 57 and the anti-reflection substrate 58 are successivelystacked thereon. When the resulting structure is pressed from above it,the thickness of the optical contacting liquid 54 between the originalplate 56 and the ND glass 57 can be made uniform within a short time,and a predetermined gap is maintained. If reconstruction light isapplied from the upper side in this state, the reconstruction light andthe diffracted light from the original plate 56 interfere with eachother in the photosensitive material 52. Thus, a hologram image of theoriginal plate 56 is duplicated satisfactorily.

FIG. 13 shows an embodiment in which spacers are disposed on therespective sides of the photosensitive material and the original plate.In this embodiment, the spacer 53 is disposed on the photosensitivematerial 52 supported by the substrate 51, and the space defined by thespacer 53 is filled with the optical contacting liquid 54. Further, thesubstrate 55 and the original plate 56 are successively stacked thereon,and the spacer 53 is disposed on the original plate 56. Then, the spacedefined by the spacer 53 is filled with the optical contacting liquid 54in the same way as the above. Further, the ND glass 57 and theanti-reflection substrate 58 are successively stacked thereon, and theresulting structure is pressed from above it, thereby allowing thethickness of the optical contacting liquid 54 between the photosensitivematerial 52 and the substrate 55 to be maintained at a predeterminedlevel by the spacer 53 and also permitting the thickness of the opticalcontacting liquid 54 between the original plate 56 and the ND glass 57to be maintained at a predetermined level by the spacer 53. By applyingreconstruction light to the stack structure in this state, a hologramimage of the original plate 56 can be duplicated in the photosensitivematerial 52.

Next, duplication of a reflection hologram will be explained withreference to FIGS. 14 to 16.

The basic structure of the reflection hologram is the same as in thecase of the transmission hologram except that the positionalrelationship between the original plate and the photosensitive materialis inverted.

In an embodiment shown in FIG. 14, a spacer 53 is disposed on areflection hologram original plate 61 supported by a substrate 51, andthe space defined by the spacer 53 is filled with an optical contactingliquid 54. On the spacer 53 and the optical contacting liquid 54 aresuccessively stacked a photosensitive material 60 supported by asubstrate 55, an ND glass 57, and a substrate 58 provided with ananti-reflection coating. Then, the resulting stack structure is pressedfrom above it. As a result, the thickness of the optical contactingliquid 54 between the original plate 61 and the substrate 55 becomesuniform. If reconstruction light is applied from the upper side in thisstate, the reconstruction light and the diffracted light from theoriginal plate 61 interfere with each other in the photosensitivematerial 60. Thus, a hologram image is duplicated in the photosensitivematerial 60.

In an embodiment shown in FIG. 15, the original plate 61, which issupported by the substrate 51, and the photosensitive material 60 areplaced opposite each other with the substrate 55 interposed therebetweenin close contact with them. Then, the spacer 53 is disposed on thephotosensitive material 60, and the space defined by the spacer 53 isfilled with the optical contacting liquid 54. Further, the ND glass 57and the anti-reflection substrate 58 are successively stacked thereon.Then, the resulting stack structure is pressed from above it, therebybringing the ND glass 57 into close contact with the photosensitivematerial 60. Thus, the thickness of the optical contacting liquid 54between the photosensitive material 60 and the ND glass 57 becomesuniform, and the photosensitive material 60 and the ND glass 57 come inclose contact with each other. If reconstruction light is applied fromthe upper side in this state, the reconstruction light and thediffracted light from the original plate 61 interfere with each other inthe photosensitive material 60. Thus, a hologram image is duplicated inthe photosensitive material 60.

In an embodiment shown in FIG. 16, a spacer is interposed between theoriginal plate and the photosensitive material, and another spacer isdisposed on the photosensitive material. The spacer 53 is disposed onthe original plate 61 supported by the substrate 51, and the spacedefined by the spacer 53 is filled with the optical contacting liquid54, and the photosensitive material 60, which is supported by thesubstrate 55, is brought into close contact with the spacer 53 and theoptical contacting liquid 54. Further, the spacer 53 is disposed on thephotosensitive material 60, and the space defined by the spacer 53 isfilled with the optical contacting liquid 54. Further, the ND glass 57and the anti-reflection substrate 58 are successively stacked thereon.Then, the resulting stack structure is pressed from above it, therebybringing the substrate 55 into close contact with the original plate 61and also bringing the ND glass 57 into close contact with thephotosensitive material 60. Thus, the thickness of each opticalcontacting liquid is maintained at a predetermined level. By applyingreconstruction light from the upper side in this state, a hologram imageof the original plate 61 is duplicated in the photosensitive material60.

Thus, when contact duplication of a hologram is to be carried out, aspacer is provided, and the space defined by the spacer is filled withan optical contacting liquid. By pressing a layer which is to be broughtinto close contact with another in this state, the thickness of theoptical contacting liquid can be made uniform within a short period oftime and maintained in this state. Accordingly, undesirable flow of theoptical contacting liquid can be eliminated, and a hologram image ofgood quality can be efficiently duplicated. Thus, the productivity canbe increased.

What we claim is:
 1. A hologram produced by applying laser light splitinto two beams to a recording unit including a photosensitive materialfilm placed in close contact with a glass selected from the groupconsisting of an anti-reflection coated glass, an ND glass, and ananti-reflection coated ND glass through an optical contacting liquid,said hologram further comprising a cushioning layer made principally ofa polymer of high elasticity, said cushioning layer being providedbetween said optical contacting liquid and said glass, so that amingling foreign substance is buried in said cushioning layer, therebyreducing the incidence of depression-shaped defects.
 2. A hologramaccording to claim 1, wherein said cushioning layer comprises as aprincipal component a high-elasticity polymer having a slope of not lessthan 0.003 μm/mgf in a stylus force-displacement measurement.
 3. Ahologram according to claim 1, wherein said cushioning layer is apolymer made of an ionizing radiation curing resin material.
 4. Ahologram according to claim 3, wherein the curing resin material is amaterial selected from the group consisting of a binder polymer ormonomer.
 5. A hologram according to claims 1, 2, 3 or 4, wherein thehologram at a portion where no depression-shaped defect is recognizedcontains a holographical record of a foreign substance observable usingan optical microscope.
 6. A hologram according to claim 5, wherein theholographical record is due to said foreign substance itself.
 7. Ahologram according to claim 5, wherein the holographical record is of aminute distortion of said cushioning layer due to said foreignsubstance.
 8. A method of producing a hologram by applying laser lightsplit into two beams to a recording unit including a photosensitivematerial film placed in close contact with a glass selected from thegroup consisting of an anti-reflection coated glass, an ND glass, and ananti-reflection coated ND glass through an optical contacting liquid,said method further comprising providing a cushioning layer madeprincipally of a polymer of high elasticity provided between saidoptical contacting liquid and said glass so that a foreign substancewhich may mingle during the production of said hologram is buried insaid cushioning layer, thereby reducing the incidence ofdepression-shaped defects.
 9. A method according to claim 8, wherein theproviding step provides a cushioning layer which comprises as itsprincipal component a high-elasticity polymer having a slope of not lessthan 0.003 μm/mgf in a stylus force-displacement measurement.
 10. Amethod according to claim 8, wherein the providing step provides saidcushioning layer as a polymer layer made of an ionizing radiation curingresin material.
 11. A method according to claim 10, wherein said resinmaterial provided by the providing step is a material selected from thegroup consisting of a binder polymer or monomer.
 12. A method accordingto claims 8, 9, 10 or 11, wherein said method provides a hologramcontaining at a portion where no depression-shaped defect is recognized,a holographical record of a foreign substance observable using anoptical microscope.
 13. A method according to claim 12, wherein theholographical record provided is due to said foreign substance itself.14. A method according to claim 12, wherein the holographical recordprovided is of a minute distortion of said cushioning layer due to saidforeign substance.